1. Field of the Invention
The present invention relates to a polyurethane having superior hydrolytic resistance, heat resistance, resistance to hot water, cold resistance, fungal resistance, mechanical performances, as well as in injection moldability, and which is useful as a material for molding, fibers and molded article comprising the same, and starting materials for preparing the polyurethane.
2. Discussion of the Background
Polyurethanes have many advantageous characteristics such as high elasticity, excellent wear and abrasion resistance, and oil resistance, and have thus been used in a wide variety of end uses, such as a replacement for rubber and other plastics.
Various types of polyurethanes are known, such as polyether-based polyurethanes, polyester-based polyurethanes and polycarbonate-based polyurethanes. These polyurethanes are widely used in the production of fibers, sheets, films, adhesives, coating agents and the like. Among these conventional polyurethanes, the polyether-based ones are superior in resistance to hydrolysis, but inferior in resistance to light, resistance to heat aging and resistance to chlorine. The polyester-based polyurethanes are superior in mechanical characteristics and wear and abrasion resistance in comparison with the polyether-based ones, but are inferior in resistance to hydrolysis and fungal resistance. Use of the polyester-based polyurethanes is limited because the surface thereof becomes adhesive or cracks within a relatively short period of time. The polycarbonate-based polyurethanes possess the same advantages described above for the polyester-based polyurethanes, and further possess superior durability. However, they are inferior in cold resistance, and are extremely expensive.
In order to improve the hydrolytic resistance of the polyester-based polyurethanes, it has been considered effective to decrease the concentration of ester groups from the polyester diol used for producing the polyurethanes. The following polyurethanes have been proposed for this purpose: (1) a polyurethane using a polyester diol, as raw material, obtained by using hexamethylene glycol and 1,10decanediol (see Japanese Patent Application Laid-open No. 173117/1985); (2) a polyurethane using, as raw material, a polyester diol comprising 2,2,4- or 2,4,4-trimethylhexanediol and adipic acid (see Japanese Patent Application Laid-open No. 713/1972); (3) a polyurethane using, as raw material, a polyester diol obtained by using 2,5-hexanediol or 2,2-dimethyl-1,3propanediol (see U.S. Pat. No. 3,097,192); and (4) a polyurethane using (2,2-dimethyl-1,3-propanedodecanedioate) glycol (see Japanese Patent Application Laid-open No. 97617/1988) .
In order to improve the hydrolytic resistance of polyester-based polyurethanes, a polyester diol which contains branched dicarboxylic acid units having one methyl side-chain has been used as a raw material to make polyurethane. For example, the following polyurethanes have been proposed: (5) a polyurethane prepared using a polyester diol and obtained by reacting a dicarboxylic acid containing 3-methylpentanedioic acid and a glycol (see Japanese Patent Application Laid-open No. 26018/1985); and (6) a polyurethane prepared using a polyester diol and containing 10 mole % or more of 2-methyloctanedioic acid of total dicarboxylic acid units (see Japanese Patent Application Laid-open No. 320302/1993).
However, with the polyurethanes described above in (1) through (4), the hydrolytic resistance is improved, but the cold resistance and low temperature characteristics such as flex resistance and flexibility decrease extremely upon standing at low-temperature because these polyurethanes have a strong tendency to crystallize. The polyurethane described in (1) obtained by using a diol having a long linear chain has the further disadvantage of low elastic recovery. The polyurethanes described in (2) through (4) using a diol having two or three methyl groups as side-chains have the further disadvantages of poor heat resistance, poor elastic recovery and poor cold resistance. Compared with conventional polyurethanes, the polyurethanes described in (5) and (6) are improved in hydrolytic resistance but are still insufficient in hydrolytic resistance and the cold resistance, heat resistance and injection moldability thereof are also considered to be at insufficient levels for practical purposes. Furthermore, compared with conventional polyurethane fibers, polyurethane fibers described in (5) and (6) are improved in heat resistance, resistance to hot water, elastic recovery, and cold resistance, but still not to a sufficient level for practical purposes. Thus, difficulties arise when these polyurethane fibers are used in combination with polyester fiber and the like, and are dyed stably and industrially with disperse dye under high-temperature and high-pressure conditions. Furthermore, the tensile strength and elongation, elastic recovery resistance to chlorine, color fastness and the like of these polyurethanes after dyeing are not sufficient for practical purposes.
As processes for synthesizing 3,8- or 3,7-dimethyldecanedioic acid, the following (7) through (9) are known: (7) a process for synthesizing 3,8-dimethyldecanedioic acid, from 2,7-octanedione comprising the five steps of Reformatsky reaction of ethyl bromoacetate, bromination of hydroxyl group, dehydrobromination, hydrogenation of double bond and hydrolysis of ester (see Ann., 580, 125-131 (1953)); (8) a process for synthesizing 3,8-dimethyldecanedioic acid, comprising seven steps starting from malonic condensation of diethyl methylmalonate and 1,4-dibromobutane, followed by hydrolysis and decarboxylation to obtain 2,7-dimethyloctanedioic acid as an intermediate and the subsequent conversion of this intermediate to acid chloride, which is then converted via diazoketone into the intended dicarboxylic acid (see Ann., 598, 1-24 (1956)); (9) a process to obtain 3,7-dimethyldecanedioic acid by hydrogenation of essential oil of Geranium macrorhizum, and subsequent ozonolysis and degradation with perchloric acid (see Chem.listy, 52, 1174-1179 (1958)).
Neither of the processes for synthesizing 3,8-dimethyldecanedioic acid described in (7) and (8) above is an industrially useful process, because many reaction steps are required, and expensive or hazardous to handle raw materials or reagents are required. The process for synthesizing 3,7-dimethyldecanedioic acid described in (9) above is also not an industrially useful process, because a natural essential oil is used as a raw material, and explosive ozone or perchloric acid is used as a reagent. Therefore, it has been strongly desired to develop a process for economically producing 3,8- or 3,7-dimethyldecanedioic acid with inexpensive raw materials and reagents through a short process.